LAMINATE WITH INNER LAYER OF CELLULOSIC FIBRES AND OUTER LAYERS OF CHIPBOARD

Abstract: The invention concerns a chipboard, its manufacture and use. The board has a middle layer containing cellulose fibre-based chaff and plastic and a wood chip layer glued onto either side of the middle layer. The board is stronger than a conventional chipboard. An extremely small hydroexpansivity is a particular advantage. The board can be used in the same way as any conventional chipboard.

Description: Laminate with inner layer of cellulosic fibres and outer layers chipboard. FIELD OF THE INVENTION The invention concerns a chipboard, its manufacture and use. BACKGROUND OF THE INVENTION Usually, a chipboard is made in such a way that a thermal¬ ly hardening urea-formaldehyde solution is mixed with wood chips and the mixture thus obtained is hardened in a hot- press. The printed patent specification FI-73717 presents a method wherein polyethylene powder is used as adhesive. Pero¬ xide, silane and a soya solution are hereby also used in the mixture. GENERAL DESCRIPTION OF THE INVENTION A chipboard has now been invented wherein the middle layer contains cellulose fibre-based chaff adhered together by plastic. The chaff may be, for example, paper chaff, wood chips or a mixture of these. The invention and some of its applications are defined exactly in the appended claims. The primary advantage of the invention is that a part of the raw material, particularly of the wood, can be replaced by cheap material and even by material available for nothing. The quantity of necessary actual adhesive is reduced at the same time. According to the invention, entirely formaldehyde- free boards can also be made advantageously. The resulting board has better properties in many respects than the conven- tional chipboard. DETAILED DESCRIPTION OF THE INVENTION The middle layer of the chipboard now invented is a mixtu¬ re of chaff and plastic where the plastic binds the pieces of chaff to one another. The piece size is, for example, 1...60 mm, usually 2...5 mm, preferably 5...10 mm. The proportion of plastic in the mixture is, for example, 5...90 %, usually 10...60 % and preferably 20...40 %. The middle layer prefera¬ bly consists of paper-based chaff. In principle, the plastic can be any polymer-based mate¬ rial which is solid at normal temperatures. The plastic is preferably a suitable thermoplastic, such as polyalkene (for example, polyethylene or polypropylene) . For example, the plastic may be process scrap, pulper scrap, recycling waste or granulate. The paper used may in principle be any suitable paper containing cellulose fibres. Cheap recycled material such as kraftliner is most advantageous. It is particularly advantageous to use chopped paper- plastic laminate as the middle layer material. Such recovered materials are available cheaply, because they are not very suitable for making recycled paper. If desired, other suitable fibrous materials may also be used together with the paper-based chaff, for example, loose cellulose fibres or wood. Additives may also be used, if required, to obtain special characteristics or to level out variations in the quality of the raw material. If desired, the chaff may even consist entirely of chopped wood. The outer board layers are made in a conventional manner of wood chips and a suitable binder. The preferable binder is a phenolic or MDI adhesive, but urea- and melamine glues, for example, can also be used. The outer layer thickness is, for example, 0.5...5 mm, usually 1...2 mm. The middle layer thickness depends on the desired board thickness, which may be, for example, 10...20 mm. The wood chips may be of a size conventionally used in the manufacture of chipboards (that is, not bigger than about 100 mm) or they may be smaller, even down to dust size, such as those used in making so-called fibreboards. The board can be made in a press in such a way that a layer consisting of a mixture of wood chips and a binder is spread out to a desired thickness on the base and on top of it a mixture of paper and plastic is spread out to a desired thickness and with a preferable moisture content of less than 8 %, preferably in a range of 1...3 %, and again on top a layer of wood chips and binder mixture. Pressing is then performed at an increased temperature. The temperature de- pends on which plastics and glues are used and it can be, for example, in a range of 110...220°C, preferably 180...200°C. The pressing time depends on the board thickness. The essen¬ tial thing is for the middle layer temperature to rise to a sufficiently high level. The pressure used can be, for exam¬ ple, 15...50 kp/sq.cm., usually about 30 kp/sq.cm. After heating, the board is cooled. Cooling, too, is preferably performed under a pressure to achieve the exact desired board thickness and for the structure not to break. When using a thermoplastic, cooling under a pressure must hereby be clear¬ ly under the melting point of the plastic and preferably also below 100°C, so that the pressure of aqueous steam will not either cause any breaking. Cooling may be performed in the same press as the heating or in a separate cooling press. The board can also be made as a pressed profile by carrying out the cooling in a mould. The board in accordance with the invention can be worked and surface-coated just like any conventional chipboard. Its strength values are at least as good as those of a conven- tional chipboard. Small hydroexpansivity is a clear advantage compared with a conventional chipboard. A board in accordance with the invention can be used for similar purposes as any conventional chipboard. It is suita¬ ble in particular for use as a surface coating or face board in structures, because a tight seam can be used due to its small hydroexpansivity. A tight seam facilitates surface treatment and improves the sound insulation. The density, which is better than in a conventional chipboard, also makes for better sound insulation. The board is also suitable for use as raw material in the furniture and building joinery industries. Example A paper-plastic laminate used for wrapping paper rolls and containing two kraft paper layers with a polyethylene film in between was chopped to a piece size of 5...10 mm and the chaff was dried to a final moisture content of 2...4 per cent. A mixture was made of wood chips and glue. A low-alkaline phenolic adhesive was used as glue. A mixture of wood chips and glue was scattered into a board press to form a blank and on top of it laminate chaff and finally a topmost layer of wood chips and glue mixture. Pressing and cooling were performed. The thickness of the wood chip layers was approximately 1 mm. The following table shows the characteristics of a board made in two ways by way of example, compared with those of a conventional chipboard. Board 1 Board 2 Conv. board Thickness, mm 1 122 1 155 15 Density, kg/cu.m. 1004 1069 700 Bending strength, N/sq.mm. 16. 8 18. 6 15 Transverse tensile strength, N/sq.mm. 0.64 0.66 0.4 Thickness swelling (2 h soaking), per cent 3.4 2.5 8 Length swelling, per cent 0.05 - 0.3

Claims: CLAIMS 1. Chipboard, characterized in that it has a middle layer containing cellulose fibre-based chaff, such as paper chaff, wood chips or a mixture of these, and plastic, so that the plastic binds the pieces together, and a wood chip layer glued onto either side of the middle layer. 2. Chipboard in accordance with claim 1, characterized in that the plastic is a thermoplastic, such as polyalkene, preferably polyethylene or polypropylene. 3. Chipboard in accordance with claim 1 or 2, characteri¬ zed in that the middle layer contains paper, preferably kraft paper. 4. Chipboard in accordance with any one of claims 1...3, characterized in that the piece size of paper and plastic, if plastic is used, is 1...60 mm, preferably 2...15 mm, most preferably 5...10 mm. 5. Chipboard in accordance with any one of claims 1...4, characterized in that the middle layer contains 5...60 per cent plastic, preferably 20...40 per cent, of the weight of the layer. 6. A method of making a chipboard, characterized in that a middle layer is made of a mixture containing paper and plastic, in which layer the paper pieces are bound together with the aid of plastic, and a layer glued of wood chips is fastened onto either side of the middle layer. 7. A method in accordance with claim 6, characterized in that the middle layer is made of paper-plastic laminate chaff. 8. A method in accordance with claim 6 or 7, characterized in that the chipboard is made in a board press in such a way that a layer containing wood chips and glue is spread out on the board, on top of it a layer containing paper and plastic and on top of the latter a layer containing wood chips and glue, whereupon the layers are pressed together, they are heated if required, they are kept compressed for a time necessary to form a board and finally they are cooled, if required. 9. A method in accordance with anyone of claims 6...9, characterized in that the moisture content of the layer containing paper and plastic is less than 8 per cent, prefe¬ rably 1...4 per cent, of the weight of the layer. 10. Use of a chipboard in accordance with anyone of claims 1...6 or made in accordance with anyone of claims 6...9, and particularly use as a face board in structures.

Inventors: MAEENPAEAE ANTTI, OLLILA TIMO, MAEENPAEAE, ANTTI, OLLILA, TIMO
Applicants: SCHAUMAN WOOD OY
Application year: 1994
Main classification: B32B5
IPC codes: B32B23